CD14 is a glycoprotein composed of 356 amino acids and anchored thereto through glycosylphosphatidylinositol (GPI) on membranes of macrophages, monocytes, Kupffer cells, neutrophiles, and partly B cells.
Human CD14 includes besides membrane-bound type CD14 (hereinafter, also referred to as “mCD14”), soluble type CD14 (hereinafter, also referred to as “sCD14” or “soluble CD14”). Furthermore, it has been reported that in blood there are a plurality of sCD14s having different molecular weights (Labeta MO: Eur. J. Immunol., 23:2144, 1993).
Human CD14 is known as an LPS receptor for endotoxins of gram-negative bacilli (Wright et al.: Science, 249:1431, 1990), which receives LPS from LBP (LPS binding protein) in blood to form a complex.
Macrophage and the like that express mCD14 are activated by a complex of LPS and sCD14 to induce production of inflammatory cytokines (Hailmann E, et al.: J. Immunol., 156:4384, 1996).
In vascular endothelial cells and vascular smooth muscle cells that do not express mCD14, production of inflammatory cytokines is induced by a complex of sCD14 and LPS (hereinafter, also referred to as “sCD14/LPS”) (Loppnow H, et al.: Infection & Immunity, 63:1020, 1995).
In addition, it reacts with bacterial cell components not only of gram-negative bacteria but also of gram-positive bacteria and with mycobacteria, and it has functions as a receptor for such as lipoteichoic acid (LTA) and peptide glycans (PepG), and reaction with above induces production of inflammatory cytokines of cells (Cleveland MG, et al.: Infect immunity, 64:1906, 1996).
Production of cytokines in cells through CD14 such as LPS or LTA exerts harmful effects on a living body and causes sepsis. Generally, in an early stage of sepsis, such symptoms as chill, hidrosis, fever, and hyposthenia are observed, and subsequently serious clinical symptoms that involve a shock are caused such as hypotension, neutropenia, disseminated intravascular coagulation syndrome, adult respiration distress syndrome, respiratory insufficiency, and multiple organ insufficiency.
As for the function of human CD14 to transduce the signal of LPS to cells, a part of the functioning region has been elucidated. The positions from 1 to 152 of the N-terminal are a region essential for expressing the function of CD14 (Juan TS, et al.: J. Biol. Chem., 270:1382, 1995) and the positions from 7 to 14 and the positions from 57 to 64 are portions essential for binding to LPS (Juan T S: J. Biol. Chem., 270, 29:17237 (1995) and Juan T S: J. Biol. Chem., 270, 10:5219 (1995)).
However, nothing has been elucidated on the function that regions from 153 to C-terminal of human CD14.
In addition, the participation of Toll like receptor (TLR) in the signal transduction of CD14/LPS to cells has been studied in recent years. To date TLR family genes composed of human TLR1, TLR2, TLR3, TLR4, TLR5 (Fernand R: Proc. Natl. Acad. Sci. USA, 95:588, 1998) and TLR6 (Takeuchi 0: Gene, 231:59, 1999) have been cloned.
Based on studies on TLR2- or TLR4-deficient mice, a possibility that TLR4 is required for signal transduction of cell components of gram-negative bacteria into cells and TLR2 is required for signal transduction of cell components of gram-positive bacteria into cells has been reported (Takeuchi O, et al.: Immunity, 11:443, 1999). Further, it has been reported that TLR2 participates in signal transduction of LPS into cells, TLR2 directly reacts with LPS on cell surfaces, and the reaction is enhanced in the presence of CD14 (Ruey-Bing Y: Nature, 395:284, 1998).
However, in the mutual action between CD14 and TLR, it has not been clarified if CD14 directly binds to TLR or a complex of TLR with accessory molecule, which is a low molecular substance whose function has not yet clarified. Further, the binding region of TLR and CD14 is quite unknown.
As the human anti-CD14 antibody that controls signal transduction of LPS through human CD14, there have been known 3C10 antibody that binds to 7th to 14th amino acids of human CD14 (Steinman: J. Exp. Med., 158: 126 (1983) and Juan T S: J. Biol. Chem., 270:29, 17237 (1995)), and MEM-18 antibody that binds to 57th to 64th amino acids of CD14 (Bazil: Eur. J. Immunol., 16:1583 (1986) and Juan T S: J. Biol. Chem., 270, 10, 5219 (1995)) are known and their application to medicaments for treating sepsis is disclosed.
Furthermore, 28C5 antibody and 23G4 antibody that inhibits binding of LPS and suppresses release of cytokines as well as 18E12 antibody that inhibits binding of LPS only partly and suppresses release cytokines have been disclosed (JP 8-510909 A).
Also, anti-CD14 antibody that is against the action of gram-positive bacteria and mycobacteria has been disclosed (JP 10-505839 A).
However, when used as a medicament for treating sepsis, an antibody that recognizes the binding region of LPS or an antibody that suppresses the binding of LPS is not expected to have an effect of suppressing signal transduction of already formed LPS/CD14. Further, it is not expected to have an effect of suppressing signal transduction by cell components of gram-positive bacteria, mycoplasma or the like, since the binding of LPS to CD14 is specifically inhibited. Further, the 18E12 antibody is not clarified with respect to the recognition site of CD14 and the mechanism of suppressing release of cytokines is also unclear.
As described above, participation of TLR in signal transduction of CD14/LPS into cells has been known. However, it is not certain as to whether or not the substance that inhibits this participation controls the signal transduction and no such inhibitory substance has been known.